Horizontal directional drilling machines are used to install underground utilities or other objects. This method is gaining widespread favor because it minimizes ground surface disruption and the likelihood of damaging already-buried objects.
Horizontal directional drilling operations generally consist of using a drilling machine to advance a drill string through the subterranean earth along a preselected path. The path is ordinarily selected so as to avoid already-buried objects such as utilities. Certain aspects of the drilling machine and the manner with which it acts on the drill string are included in U.S. Pat. No. 6,085,852 and U.S. Pat. No. 5,799,740, the contents of which are incorporated by reference herein.
The drilling machine generally comprises a frame, an anchoring system, a drive system mounted to the frame and connectable to the uphole end of the drill string, and a bit connected to the downhole end of the drill string. The drive system provides thrust and rotation to the drill string which, in turn, thrusts and rotates the boring tool through the subterranean earth, forming a borehole. The drive system generally comprises one or more power sources for thrusting and rotating the drill string. The boring tool is advanced in a substantially straight line direction by rotating and thrusting the drill string with the drive system. To change the direction, conventional steering techniques are used such as are associated with a slant-faced bit. This type of bit is, after being oriented in the desired direction, advanced without drill string rotation to change the course of the borehole.
The drill string is extended by adding a series of drill pipe sections to the drill string. A signaling tracking device, or beacon, is conventionally placed in the boring tool at the downhole end of the drill string. In this manner, an above-ground remote operator can, with the assistance of a hand-held transceiver device (commonly referred to as a walk-over tracking device), monitor the location of the boring tool as it is extended to form the borehole.
When the borehole is completed, typically the bit is replaced with a backreaming tool which is pulled back through the borehole to pack and finally size the borehole. The tracking device and beacon may or may not be used to track the backreaming tool.
There are times when the operating personnel must gain access to the downhole end of the drill string, such as by excavating a pit where the boring tool is expected to cross above or below an existing underground object, such as a pipeline. The operator of the tracking device can then visually observe the approaching boring tool so as to ensure it is on a drilling path that will not collide with the underground object. At other times, the operator must gain access to the downhole end of the drill string in order to replace a worn or broken boring tool or at the end of the bore, replace the boring tool with a backreaming tool. At these times it would be useful for this remotely positioned operator to have some means for stopping or preventing advance and/or rotation of the drill string. As will be seen below, the present invention fulfills this need.